NL8300587A - METHOD FOR TREATING EXHAUST GAS - Google Patents

Description

* · * T VO 4037 * ......

Method for treating exhaust gas.

The invention relates to a process for treating exhaust gas, in order to reduce the concentration of harmful substances by oxidation.

Thermal post-combustion (TNV) is known as a method for the oxidative decomposition of harmful substances in exhaust gases.

This series of fundamental investigations for the TNV of harmful substances shows that in a predominantly number of cases the attunement of the TNV device to the oxidation conditions of the intermediates (secondary harmful substances) mainly leads to the formation of carbon monoxide (CO), which requires high operating temperatures, which are clearly above 750 ° C.

Particularly for pollutants belonging to emission class III of the "Technische Anleitung zur Reinhaltung der Luft" (hereinafter TALucht), the permissible residual concentrations of the 15 primary pollutants (300 mg / m3) can already occur at temperatures between 500 and 600 ° C, while a permissible residual CO concentration of up to 100 mg / m3 (norm-m3) can only be reached above 800 ° C.

In practice, these conditions are still sharpened everywhere in those cases, in the course of time, deposits build up on the wall in the combustion chamber, so that the CO oxidation can be inhibited and possibly even higher temperatures are required to treat the exhaust gas.

To clean up the secondary pollutants, the exhaust gas must therefore be treated at considerably higher temperatures than would be necessary for the removal of the primary pollutants per se. This necessity makes the usual treatment of exhaust gas, both technically and economically, considerably more cumbersome than it should have been for the actual cause.

Thus, there was a need to have an exhaust gas treatment method which would allow, on the one hand, to limit the emission of harmful substances to the permissible level and, on the other hand, to achieve a significant improvement in technical and economic terms.

A special need was to improve existing 8300587 »2 TNV devices by simple measures in the sense indicated.

The said need is met by a process for treating off-gas to reduce the concentration of harmful substances by oxidation, which process is characterized in that a) off-gas is heated in a first stage with energy supplied from the outside and partially oxidizes, then b) catalytically treating the gas stream from step (a).

The present process for treating exhaust gas is a 2-step process.

In a first stage, exhaust gas containing harmful substances with externally supplied energy is heated and partially oxidized. This first stage is preferably a thermal post-combustion known per se.

According to the invention, the gas stream from the first stage, which already forms the clean gas in the usual process, is treated catalytically in a second stage.

According to a preferred variant, a further stage for recovering heat is provided for vddr and / or after the second stage.

Oxidation catalysts known per se can be used as catalysts. These can be used in all known forms, e.g. as a fabric, mesh or sieve or as a bulk material of particles formed and not formed. Preferably, catalysts based on metal oxide and / or precious metal are fixed on porous supports, the support preferably being in the form of pearls, as extrudate or in honeycomb form. Such catalysts are available commercially.

With the present method, exhaust gases can be treated, which contain the most diverse primary harmful substances. Particularly suitable as primary pollutants are individual or several of the following compounds: saturated aliphatic hydrocarbons, such as e.g. n-hexane and n-octane, 35 - unsaturated aliphatic hydrocarbons, such as e.g. ethylene and butadiene, 8300587 Λ -Λ 3 - aromatic hydrocarbons, such as e.g. benzene, toluene, xylene, styrene and ethylbenzene, mixtures of aliphatic and / or aromatic and / or naphthenic hydrocarbons, such as e.g. solvents based on gasoline or turpentine, 5-aliphatic alcohols with one or more hydroxyl groups, such as e.g.

methanol, ethanol, n-propanol, i-propanol, n-butanol, diacetonal alcohol, ethylene glycol and propylene glycol, aromatic compounds substituted with hydroxyl groups, such as e.g. phenols and cresols, 10-ethers, such as e.g. alkyl glycols (methyl, ethyl, propyl and butyl glycol), cyclic ethers (ethylene and propylene oxide), aldehydes such as e.g. formaldehyde and acetaldehyde ketones such as acetone, methyl ethyl ketone and cyclohexanone esters such as e.g. glycerides, esters of his acid (preferably methyl-ethyl or n-butyl esters), and - organic acids or anhydrides thereof, such as e.g. formic acid, acetic acid and phthalic acid and maleic anhydride.

Secondary harmful substances are formed from such primary harmful substances by partial oxidation, such as e.g. form-20 aldehyde or acetaldehyde, in particular carbon monoxide (CO). The present method makes it possible in particular to efficiently limit the content of secondary harmful substances.

A special variant of the present method consists in the technical and economic improvement of pre-existing single-stage devices for the treatment of exhaust gas, in which exhaust gas is purified and heated in a single stage using energy supplied from outside. treats the exhaust gas in the already existing stage with less energy supply and subsequently treats the gas stream thus obtained catalytically. The stage already existing is preferably a thermal post-combustion device.

Substantial advantages can be achieved by the present method, such as e.g.

a) a reduction of the externally supplied energy in the first stage. On the one hand, this leads to considerable cost savings, which - in combination with a temperature control determined as a function of the process - can amount to 50% of the energy costs required so far for the first stage. On the other hand, the lower temperature can make it possible to use cheaper construction materials.

5 b) Increasing the flow rate. Due to the subsequent catalytic treatment, the influences of the residence time, which are known in thermal afterburners, are no longer disadvantageous.

Compared to such known devices, larger quantities of exhaust gas and / or harmful substances can be obtained at lower operating temperatures with an equally good final combustion result. By adapting existing devices in the present sense, an increase in production can be achieved without having to install an entirely new exhaust gas treatment device.

15 c) Remediation of existing establishments. The existing establishments that no longer meet the legal requirements or can only meet them with high costs can be adapted to the legal requirements without having to make large investments.

The present method is further described by the following examples.

The device used for carrying out the tests is schematically shown in Fig. 1. The exhaust gas to be purified is fed through a pipe (1) via a heat exchanger (2) to a pre-chamber (3), from which the ends up in the first treatment stage for the exhaust gas (4), namely a combustion chamber with a volume of 275 1. Through line (5) fuel (a mixture of propane and air) is also fed to the first through a combustion nozzle (6). treatment step (4) is supplied and burned there in an open flame (7). The resulting gas mixture, which contains primary and secondary pollutants, ends up in the heat exchanger (2) via line (8 / A) and from there into the second exhaust gas treatment stage (9), in which a catalyst (10) was applied. Otherwise, the gas leaving the combustion chamber via line (8) can be supplied to the second stage (9) via (8 / B), i.e. without passing through the heat exchanger 35. The catalytic after-treated gas (clean gas) is supplied via line (11/0) to the 8300587 * * 5 exhaust gas chimney (not shown). The clean gas leaving the second stage (9) can otherwise, with a sufficiently large heat -content, are fed via line (11 / D) to the heat exchanger (2) and thus be used for preheating the exhaust gas to be purified.

Air was used as the exhaust gas to which 1000 ppm of n-hexane as a harmful substance had been added. The flow rate varied between 70 and 100 Nm3 / hour, at a volume rate of 20,000 l / h per liter of catalyst.

In the case of n-hexane, the bulk material catalysts used were catalysts, the catalyst KCO-1922 K / M being an oxidation catalyst of the palladium / manganese type on an A 2 O 3 support, and the catalyst KCO -3366 K / M an oxidation catalyst containing platinum as the active component. Both catalysts are commercially available (Kali-Chemie company). In the other examples, the honeycomb body catalyst KCO-WK-220 ST (Manufacturer Firm Kali-Chemie), a platinum-based oxidation catalyst, was used as the catalyst.

20 samples were taken each time before and after the second stage (9) to analyze the gas mixtures.

Fig. 2 shows the measurement results of two test series for n-hexane as a harmful substance, the concentration of harmful substance being shown as a function of the temperature when leaving the combustion chamber. When using only the TNV, so according to the known method (empty circles or triangles in fig.

2), the class III limit value for the harmful substance was reached at about 610 ° C. However, in order to reach the legally prescribed limit of the TA air, the TNV had to operate at approx. 860 ° C due to the high CO concentrations. The present method (filled circles 30 and triangles in fig. 2), on the other hand, made it possible to operate at 600 ° C? by recording the residual CO concentration, the combustion room temperature could even be reduced to about 540eC, since already at this temperature the permissible emission limit value of 300-35 mg / m3 was not exceeded in terms of both the sum of the primary and secondary pollutants, and also with regard to carbon monoxide, clearly below the permissible emission limit value of 100 mg / m3, 8300587% 6 was found. Therefore, a temperature reduction of about up to 320 ° C can be achieved by the present process.

The results of further test series are brought together in the tables below, where the cumulative composition of clean gas (100 corresponds to the total amount of carbon present in the harmful substance used) as a function of the temperature at the exit of the combustion chamber (T, a) is shown for the thermal afterburning only (TNV) and for the present method (TNV / KNV). The test parameters are shown after each table. The abbreviations used in the tables have the following meanings: S = harmful substance; ZP = carbonaceous organic intermediates, e.g. formaldehyde.

To meet the requirements of the TAL air, the downstream catalyst treatment allowed the combustion chamber temperature to be reduced from above about 800 ° C to 600 ° C (Table A), 570 ° C (Table B) and 480 ° C in each case. (Table C). Similar results can also be seen from the further tables.

A comparison of Tables A and B shows that an increase in the flow rate in the conventional method requires a significant increase in the temperature of the combustion chamber, while in the present method, on the other hand, the same temperature can be used.

TABLE A Oxidation of n-hexane

25 TBK, a TNV TNV / KNV

[° C] S ZP C02 CO S ZP C02 co 500 41 30 12 17 19 0 79 2 550 30 18 19 33 12 0 86 2 30 600 22 12 26 40 7 0 91 2 650 16 10 36 38 5 0 93 2 700 10 7 50 33 3 0 95 2 750 5 2 65 28 2 0 97 1 800 2 0 76 22 2 0 98 0 8300587 è '7

Footnote to Table A.

harmful substance: n-hexane harmful substance concentration: 1000 ppm flow rate: 95 Nm3 / hour

5 catalyst KCO-1922 K / M

TABLE B Oxidation of n-hexane

TBK, a TNV TNV / KNV

t ° C] S ZP C02 CO S ZP C02 co 10 400 40 35 10 15 29 22 38 2 450 43 26 12 19 17 18 63 2 500 20 24 21 25 10 10 78 2 550 16 9 36 39 7 3 88 2 600 8 2 62 28 5 2 91 2 15 650 4 0 78 18 3 0 95 2 700 3 0 86 11 3 0 96 1 750 2 0 90 8 2 0 97 0 pollutant: n-hexane pollutant concentration: 1000 ppm 20 flow : 73 m3 / hour

catalyst: KCO-1922 K / M

8300587 - - 8 TABLE C Oxidation of n-hexane

TBK, a TNV TNV / KNV

. [° C] S ZP C02 CO S ZP C02 co 5 400 59 11 17 13 22 0 76 2 450 52 11 21 16 14 0 84 2 500 31 9 26 34 7 0 91 2 550 14 5 39 42 4 0 94 2 600 7 7 53 33 2 0 97 1 10 650 4 4 72 20 1 0 98 1 700 2 0 86 12 1 0 99 0 750 1 0 89 10 0 0 100 0 pollutant: n-hexane pollutant concentration: 1000 ppm 15 flow : 73 Nm3 / hour

catalyst: KCO-3366 K / M

TABLE D Oxidation of benzene

TBK, a TNV TNV / KNV

[° C]

20 S ZP co2 CO S ZP co2 CO

100 100 0 0 0 100 ooo 150 88 0 12 0 200 22 0 78 0 250 10 0 90 0 25 300 6 0 94 0 350 3 0 97 0 400 1 0 99 0 450 0 0 100 0 500 30 550 600 650 100 0 0 0 8300587 9 TABLE D (Continued)

Oxidation of benzene

TBK, a TNV TNV / KNV

[° C] S ZP C02 CO S ZP C02 co 5 700 91 2 4 4 750 1 0 33 66 800 0 0 '95 5 850 0 0 100 0 0 0 100 0 harmful substance benzene 10 harmful substance concentration: 1000 ppm space velocity: 20 Ito3 / hr / l catalyst

catalyst: KCO-WK-220 ST

The first treatment step (4) was heated indirectly.

TABLE E Oxidation of Methyl Acetate

15 TBK, a TNV TNV / KNV

[° C] S ZP C02 CO S ZP C02 co 100 100 0 0 0 100 100 150 96 0 4 0 20 200 86 4 10 0 250 67 3 30 0 300 40 2 58 0 350 20 1 79 0 400 100 0 0 0 9 0 91 0 25 450 99 1 0 0 2 0 98 0 500 98 1 1 0 0 0 100 0 550 96 2 2 0 600 94 3 3 0 650 90 4 3 3 30 700 54 4 6 36 750 7 0 16 77 800 0 0 96 4 850_0_0 100_0_0_0 100_0_ 8300587

J V

10

Footnote to Table E

harmful substance: methyl acetate concentration of harmful substance: 2100 ppm space velocity: 20 Nm3 / hour / 1. catalyst

5 catalyst: KCO-WK-220 ST

The first treatment step (4) was heated indirectly.

TABLE · F Oxidation of benzene

TBK, a TNV TNV / KNV

[° C] 10 s ZP C02 COS ZP C02 co 400 59 0 31 10 7 0 93 0 450 57 0 N31 12 5 0 95 0 500 53 0 33 14 4 0 96 0 550 46 0 37 17 2 0 98 0 15 600 35 0 - 40 25 1 0 99 0 650 27 0 45 28 0 0 100 0 700 19 0 69 12 750 12 0 82 6 800 4 0 93 3 0 0 100 0 20 pollutant: benzene pollutant concentration: 900 ppm flow rate : 75 Nm3 / hour

catalyst: KCO-WK-220 ST

TABLE · G Oxidation of methyl acetate

25 TBK, a TNV TNV / KNV

[eC] S ZP C02 CO S ZP C02 co 400 57 7 28 8 17 0 83 0 450 54 8 28 10 14 0 86 0 30 500 46 13 26 15 10 0 90 0 550 34 19 26 21 5 0 95. 0 8300587 Ϋ> 11 TABBL G (Continued)

TOK, a TNV TNV / KNV

C ° C] S ZP C02 CO S ZP C02 co 600 22 9 35 34 2 0 98 0 5 650 15 3 48 34 1 0 99 0 700 10 1 66 23 0 0 100 0 750 6 0 89 5 0 0 100 0 800 2 0 98 1 0 0 100 0 harmful substance: methyl acetate 10 harmful substance concentration: 2200 ppm flow rate: 75 Md3 / hour

catalyst: KCO-WK-220 ST

TABLE H Oxidation of n-hexane

TOK, a TNV 'TNV / KNV

15 [° C]

S ZP C02 CO S ZP C02 CO

400 52 10 19 19 7 0 93 0 450 47 10 23 20 7 0 93 0 500 42 13 19 26 5 0 95 0 20 550 28 3 27 42 3 0 97 0 600 .12 1 47 40 0 0 100 0 650 6 0 69 25 700 3 0 87 10 750 2 0 92 6 25 800 2 0 94 4 0 0 100 0 harmful substance: n-hexane harmful substance concentration: 1000 ppm flow rate: 75 Nm3 / hour

catalyst: KCO-WK-220 ST

8300587 12 ✓ · * l

Good results were also obtained with mixtures of harmful substances which were treated according to the present process. Surprisingly, the temperature in the combustion chamber could even be lowered below those temperatures which were determined as lower limit temperatures during the treatment of the individual components.

According to another variant of the present method, a part of the exhaust gas is not treated in the first stage, but is passed through it via a bypass. In a device according to Fig. 1, said bypass can be designed, for example, as a direct connecting pipe between the pipe (1) and the pipe (8 / A) and / or (8 / B) and may also contain means known per se to control the flow to arrange.

It has been found possible to pass up to 60% by volume and in particular up to 50% by volume of the total flow of exhaust gas through said bypass.

8300587

Claims (5)

Method for treating exhaust gas for reducing the concentration of harmful substances by oxidation, characterized in that a) exhaust gas is heated in a first stage with energy supplied from the outside and partially oxidized, and subsequently b) the gas stream obtained from step (a) is catalytically treated. A method according to claim 1, characterized in that the treatment according to step (a) is a thermal post-combustion. 3. Process according to claim 1 or 2, characterized in that the catalytic treatment is carried out before and / or after a heat recovery step. 4. Process according to claims 1-3, characterized in that a metal oxide and / or a noble metal catalyst is used as the catalyst. 15 Method for improving existing one-stage exhaust gas treatment devices, wherein exhaust gas is purified and heated in one stage using energy supplied from the outside, characterized in that the exhaust gas in said stage is supplied with less feed of energy and additionally catalytically treats the resulting gas stream. 8300587